Elastomerics Round Up

Flexible plastics, or elastomers, are versatile and necessary for a broad range of applications. A huge variety of polymer chemistries are involved in achieving elastomeric properties. This report provides a roundup of technologies and industry news categorised under the following groups: absorbable elastomers, valves, PVC, silicones, TPEs and TPUs.

Absorbable Elastic Polymers

Strataprene SVG12, produced and marketed by US-based custom polymer manufacturer Poly-Med Inc, is a high molecular weight polymer prepared from a number of FDA-recognised monomers and is already used in compliant medical devices on the market. The polymer is designed to be both tough and elastic while being fully resorbable. It can be processed into a variety of constructs such as films, fibres, and coatings. Once in these forms, the elastic nature of the polymer allows for novel uses of resorbable materials. The polymer can be useful for indications associated with elastic materials—such as barrier or fixation materials—or areas associated with resorbable materials, like drug delivery or limited-term strength retention.

Poly-Med Inc says that Strataprene SVG12 is commonly prepared into a film. In this form the material is fully transparent, nearly amorphous, and free from defects. Additionally, the films are highly compliant and elastic. Thus, they easily assume the shape of surfaces to which they are applied. Tensile analysis of such films indicates that the modulus values approach 8.5 Mpa (85 bar or 1,233 psi), which is far softer than most surgical films on the market and is closer to that of human tissue.

Traditional bioresorbable materials are said to be stiff and lack a significant ability to plastically deform—these samples fail by crack propagation soon after the onset of failure. Strataprene SVG12, on the other hand, is said to demonstrate a high degree of extension prior to rupture. Films exhibit a yield strain of up to 41.5% and an ultimate strain of 1,000% while resisting fatigue in the elastic region. Thus, in this form highly compliant Strataprene SVG12 films show significant promise as flexible barrier films in a dynamic in vivo environment.

Valves

Vial Component Enables Airtight Seal for Needle-Free Syringes: Italy-based device manufacturer Haemopharm Healthcare has developed an airtight rubber seal for glass vials and needle-free syringes called NIV. The device is particularly useful for formulations which require reconstitution, mixing or transfer before administration to the patient.

In traditional vial seals, the rubber top protects the contents from outside contamination. Needles pierce the rubber stopper easily, allowing access to the medication. When medication is drawn from a rubber-topped vial, users must follow time-consuming procedures to prevent contamination and avoid backflow and dangerous aerosol release from the vial.

With NIV, when a syringe is removed the seal automatically closes and creates an airtight seal on top of the vial. This device is designed to replace both standard vials used with normal needle-based syringes, as well as needle-free vial connectors or adaptors which require additional components for drug reconstitution. The latter are generally very expensive.

NIV won a Best Innovation prize at the recent CPhI pharmaceutical trade show in Madrid.

Speaking about valves, Netherlands-based specialist valve moulder Minivalve International utilises the versatile properties of elastomeric materials for their miniature valve components. The company’s products can be as small as a 1.5 mm diameter one-way valve.

Their valves are designed to replace complex multi-component one-way and relief valve systems.

Minivalve’s product line is made of monolithic elastomeric material, allowing for a much more compact, lower cost build with what managing director Peter Nijland describes as a “surprising performance”.

He says: “The design of the physical properties of the elastomer material such as hardness, modulus, elongation and resilience are carefully balanced against constructive design elements to achieve optimal valve performance.”

Interestingly, Minivalve makes use of the elastic properties to create undercuts in parts that are impossible to make in plastic, while still allowing the components to release from the high cavitation moulds.

PVC

Evonik Invests in Phthalate-Free Plasticiser Production: German chemical company Evonik has announced that it will invest a sum in the region of “double digit millions of Euros” at its facilities at the Marl Chemical Park in Germany to produce a new range of phthalate-free and bio-based PVC plasticisers.

Production of the plasticiser—1,2-cyclohexane dicarboxylic acid diisononyl ester—will begin in the second half of 2013. An annual 40,000 tons will be produced in Marl. Evonik began building the production facilities at the Marl Chemical Park this summer.

Evonik says that consistent research will successively add additional innovative products to the new generation of plasticisers. These plans include the launch of bio-based plasticisers.

Nexeo to Distribute Resilia Kem One’s Nakan Medical PVC in UK and Ireland: Nexeo Solutions, a global plastics distributor with 2,300 employees, is the new UK and Ireland distributor of Resilia’s Nakan range of healthcare PVC compounds.

Resilia, part of the recently formed Kem One vinyls group, is a leading European producer of PVC compounds. Its Nakan medical products comply with European Pharmacopoeia and USP testing. The Nakan medical range includes a variety of compounds, including ones for resilient extrusion for peristaltic pump applications, ETO and gamma resistant types for blow moulding, as well as phthalate-free and self-frosted effect compounds.

Kem One have named former Resilia general manager Marco Toscano as chief operating officer for the Innovative Vinyls division and a member of Kem One's executive committee (see page 6 of the January-February 2013 print edition of Medical Plastics News).

USA-based sustainable healthcare members association Practise Green Health has launched a DEHP-Free Award. The award will be given to a hospital or system that demonstrates the most success with replacing DEHP-containing medical devices with alternatives, particularly where there are vulnerable patient populations.

USA-headquartered Teknor Apex has developed a DEHP-free PVC film, according to a recent report on medtech supplier website Qmed.

The plasticiser used is a citrate. Rob Fisher, director of sales in Teknor Apex’s vinyl division, explains: “Citrate plasticisers provide similar benefits to phthalates for device manufacturers with respect to both the performance of the device as well as the manufacture and assembly of the device.”

Talking of new films, Vancive Medical Technologies, formerly Avery Dennison Medical Solutions, has developed a polyolefin film for ostomy bags, InteliShield Barrier Film, which it is marketing as DEHP- and PVC-free.

The film structure has two odour blocking technologies. In addition to a traditional passive oxygen barrier layer that blocks odouriferous molecules based upon their size, InteliShield also incorporates an organic chemical in barrier layers that traps larger molecules due to their shape and size.

Silicones

Silicone Moulding Vulcanises Fakuma: In November, a number of injection moulding machine manufacturers demonstrated their companies’ prowess in silicone moulding machinery at Fakuma—Germany’s second largest plastics trade show.

Germany’s Arburg unveiled its twin screw Injester module for the processing of solid silicone (HTV—high temperature vulcanisation) and other high viscosity materials.

A key aspect of the machine is its pair of counter-rotating, servo-electrically driven screws (see bottom left image). These work together to ensure gentle material feed at a constant pressure resulting in, according to Arburg, a high level of process reliability and part quality. The screws convey the HTV compound continuously and without bubbles via the pressure-regulated material feed of the injection unit.

Arburg state that refilling is possible with ease during the running process. The twin-screw Injester is also said to be quick and easy to clean. This advantage is particularly useful in the case of single-component silicone, where frequent material changes are often necessary.

The Injester is compatible as a module on Arburg’s Allrounder injection moulding machine.

Austria’s Engel demonstrated UV vulcanisation of silicone at Fakuma.

UV vulcanisation enables silicones to be combined with a wide range of temperature sensitive thermoplastics via twin shot and overmoulding, including polypropylene (PP).

A key aspect of UV vulcanised silicone moulding is in the mould itself. Here, UV light is produced by UV lamps which have been integrated in the mould. The light is transmitted into the cavities where the silicone parts form via plastic inserts. Engel’s partner Elmet in Austria supplies the UV lamps and inserts. UV vulcanisation can also facilitate reductions in cycle times.

In the field of traditional liquid silicone rubber (LSR) moulding, Engel’s head of medical, Christoph Lhota, has co-authored a technical report on medical applications of moulded LSR. In the report, Christoph highlights interesting applications for the material through case studies.

The case studies include dialysis filter sealing rings manufactured by Fresnius Medical Care in Germany; needle-free connectors from device makers ICU Medical and Becton Dickinson in the USA, and B Braun in Germany; CPAP (continuous positive airway pressure) respiratory masks produced by Norway’s Laerdal (see image middle-right); a hormone releasing vaginal ring from Germany’s MDS; silicone-based tear duct implants for precise medication dosage; implantable Neuflex prosthetic joints from USA-headquartered DePuy (top right); and Ahmed implantable glaucoma valves from USA-based New World Medical. For a copy of the report please contact the editor at sam.a@rapidnews.com.

Germany’s Ferromatik Milacron, a subsidiary of USA-based plastics machinery manufacturer Milacron, used an Elektron 50 moulding machine with a clamping force of 500 kN to produce transparent baby pacifiers at Fakuma in a single shot, made entirely of silicone. The shot weight was 20 g. In contrast to conventional two-component pacifiers (ABS and LSR) all-silicone pacifiers are manufactured as a single part, reducing production costs.

On the subject of moulding, dry ice cleaning is recommended by USA-headquartered dry ice specialists Cold Jet, particularly when manufacturing LSR parts with thin wall sections and multiple undercuts.

According to Cold Jet, it is critical to keep the mould vents clean for proper mould venting. LSR’s low viscosity results in very high injection speeds which tend to cause dieseling or scorching at the end of fill. This low viscosity also causes LSR to flash more readily than thermoplastics. Traditional vents for thermoplastics are small, but they are even smaller for LSR resins—making them difficult to clean properly and quickly with traditional cleaning methods. However, small, shaved dry ice particles enable an easy vent clean, reducing the chances of gas trapping in the mould.

Cold Jet recommends its SDI Select 60 dry ice system for cleaning tight tolerance silicone moulds.

Silicone Compounding News: In November 2012, USA-headquartered specialist silicone compounder NuSil completed the fourth phase of expansion at its facility in Bakersfield, California. The newest building is NuSil’s fourth on a 15-acre campus. It covers 35,000 sq ft (3,252 sq m) of land and is part of a multi-year plan to expand to a total of seven buildings.

NuSil also recently broke ground on the fifth phase of the expansion, with two new buildings and an additional 80,000 sq ft of manufacturing space scheduled to be completed in 2013 and 2015.

NuSil is a specialist compounder of silicones with active pharmaceutical ingredients (APIs). In particular, it is an expert in the modification of silicone chemistry and its influence on release rates of active pharmaceutical ingredients (APIs).

This expertise is evidenced in a case study published by NuSil. The company fabricated the antibiotics rifampin and minocycline into a formulation which was then moulded into a component that maintained mechanical strength according to some fairly challenging elution parameters. Both drugs needed to be completely released after 14 days with elution profiles (the rate of elution over time) which were approximately the same.

In a process which comprised multiple phases of formulation, encompassing over 100 elution studies, a highly advanced compound was eventually developed which met these criteria. The project was described by NuSil in an interview with Medical Plastics News as being one of the top healthcare research activities over the past two years.

Some of the compounding challenges overcome by NuSil were as follows. The polymer backbone was carefully selected to allow drugs to freely travel within the compound. It was realised after the first attempt that a fluoro-silicone backbone blocks pathways and makes it difficult for the drugs to pass. Optimised levels of reinforcing filler and crosslink density further enhanced permeability.

Lower temperature curing was achieved using a competitive inhibitor instead of a fugitive inhibitor.

And an optimised mix of pharmaceutical grade excipients was added to facilitate improved elution after other excipients were ruled out because they resulted in a tackier raw material that diminished processability.

Overall, in addition to developing a highly effective antibiotic eluting mouldable silicone compound, NuSil concluded that silicone chemistry lends itself very well to optimisation and that modification of the formulation influences the release of actives while maintaining processability. For more details of the case study please contact the editor at sam.a@rapidnews.com.

In other news from NuSil, the company has launched a new range of heat-cure coloured inks, MED-6613-X. The newly released colours—red, white, green, bright blue and dark blue—are suitable for devices intended for implantation for more than 30 days. NuSil says the inks vastly expand the company’s existing colour palette and provide more vibrant, creative marking options.

On the subject of silicone compounding, US-headquartered Saint-Gobain Performance Plastics are promoting the advantages of working with a custom compounder when developing a new device design.

According to the company’s marketing manager, Aaron Updegrove, working with a knowledgeable supplier from the design stage can help manufacturers identify the material best suited for specific applications, and create a formulation tailored to optimise end product performance.

Another medical grade silicone manufacturer, Bluestar Silicones with headquarters in France, presented a new range of biocompatible silicone skin adhesives, Silbione HC2, to be used on breached skins and open wounds at the Compamed trade show in November.

According to Bluestar Silicones, both are tacky gels with excellent balance between skin adhesion and atraumatic removal.

In June 2012, Bluestar Silicones was awarded the Frost and Sullivan 2012 Product Differentiation Excellence Award in Healthcare Applications for its silicone foam technology, Silbione RT foams.

Silbione RT foams are liquid materials with lightweight, breathable, flexible and weather resistant properties to weathering.

US silicone manufacturer Dow Corning has written about the importance of China’s healthcare sector as a key growth area, referring to some impressive trade statistics. The Chinese medical device market grew by 27% to US$22 bn in 2011. Chinese exports grew by 20% to reach US$8 bn in 2010. The full report is available on www.mpnmagazine.com.

Silicone Moulders: France-based Top Clean Packaging has mastered twin-shot LSR moulding.

The “bi-injection” of two densities of LSR has been done in a single step process. The technology, said to be the first in the world, has been developed by the Italian branch of Top Clean Packaging.

Being a thermosetting compound, LSR is difficult to be overmoulded in a two-step process, as it requires a coreticulation and not a fusion process for bonding. However, in a rotary mould it is possible to combine on the same machine two different hardnesses of silicone, or two grades with different properties, allowing production of parts with a structural frame of harder material, as for example 60/70 shore A, with a softer, more comfortable and flexible grade, maybe 30 shore A.

Top Clean says this technology can be used to produce respiratory face masks for applications like oxygen therapy, with a hard frame and soft skin-contact part, in a single step. Similarly, the technology can be used to combine standard silicone grades with semiconductive grades to make valves with a self-diagnostic feature.

Top Clean are also able to overmould silicone over thermoplastic, for example, a PBT, using a rotary twin-shot mould. The mould comprises: a hot runner system which allows injection of plastic without requiring removal of the hot runner; and a cold runner system to overmould a “microinjection” of silicone rubber.

TPEs

Polyisobutylene-based Drug Eluting TPEs for Breast Reconstruction and Cancer Treatment: According to a recent report on US science news website LiveScience.com, published with support from the USA’s National Science Foundation, a team of researchers from the University of Akron in Ohio have developed a new type of material that can be used as the shell of a breast implant. Diagnostic agents that help reveal the presence of cancer cells, as well as cancer-fighting drugs and painkillers, can be embedded into the shell and released into the body.

“We are trying to integrate breast reconstruction with cancer treatment,” said Judit E Puskas, University of Akron professor of chemical and biomolecular engineering, who is leading the project.

The TPE is polyisobutylene-based, which means it is similar to butyl rubber, or synthetic rubber. It exhibits advantages over silicone, the current material used in breast reconstruction, in that it is lighter and stronger. Compared to other rubbers, the TPE is especially impermeable, preventing liquids from seeping through—essential for prevention of gel leakage in an implant.

On November 30, 2012, technical research engineer Giles Meakin from UK-based minimally invasive surgical device manufacturer Surgical Innovations plc presented a summary of joint research work conducted on tri-block copolymer TPEs at the University of Bradford, also in the UK.

Previously Giles was an associate belonging to a Knowledge Transfer Partnership (KTP) between the University of Bradford and Surgical Innovations.

Working closely with the university’s polymer research centre—Polymer IRC—the goal was to develop TPE compounds with specific properties related to elasticity and recovery rates, gas permeability, sterilisation resistance and chemical and lipid resistance.

The specific material was also required to meet specific biocompatibility and extractable and leachable requirements for ISO10993 and United States Pharmacopaeia (USP) regulations respectively.

Advantages gained via the partnership included Surgical Innovations lending extinct mould tools to the university’s polymer department to help aid in academic projects carried out by final year and masters students. At the same time, the university’s polymer department provided the expertise and facilities including support in the form of MoldFlow simulation software to the KTP project.

As a result of the project, Surgical Innovations say they have found new areas of usage for TPEs, giving potential savings in manufacturing of up to £40,000 a year. They also state that there is scope for more research into TPEs and PEEK.

US polymer compounder and distributor PolyOne is promoting the use of TPEs for ergonomic enhancement in medical device design. Ergonomic considerations, also called human factors, are of importance anywhere on a device where a human operator makes contact, for example handles, knobs, buttons and orthotic pads.

Traditionally, TPEs have been used in order to provide grip. But recently, according to PolyOne, they are being used to protect device operators from injury when using equipment which requires forceful exertions, repetitive motions, contact stresses and vibration.

Larry Johnson, global healthcare marketing director at PolyOne told Medical Plastics News: “Hospitals are intense and demanding environments. Ergonomic considerations give more benefits than just good grip. They can help to prevent problems like arthritis and carpal tunnel syndrome.”

Thanks to the fact that TPEs are soft to the touch and adhere very well to a number of rigid plastics like PC/ABS, they are used extensively in hand-held devices.

In 2011 the FDA released a draft guidance document called Applying Human Factors and Usability Engineering to Optimize Medical Device Design. The guidelines, spanning 37 pages, aim to improve the safety and effectiveness of medical devices. They recommend a number of tests which can be performed to demonstrate ergonomic safety. It also identifies examples of medical devices which have already been optimised ergonomically for improved usability. While the guidance is currently non-binding for manufacturers in the US market, there are reports that some manufacturers are anticipating a future form of mandatory regulation regarding human factors in medical device design to protect the safety of users.

Two series of biocompatible TPEs—6042 MD and 6003 MD—have been added to US-headquartered compounder RTP Company’s range of healthcare compounds. The compounds have been pre-tested for compliance with the three most common parts of ISO10993: part 5, in vitro cytotoxicity; part 10, irritation; and part 11, systemic toxicity. These tests are the first data points that help to establish a pattern of concern for safety to the FDA and EU industry regulators and provide confidence that the finished, moulded and assembled device will also pass biocompatibility testing. RTP can provide a statement of biocompatibility to customers.

Naturally opaque, the new TPE compounds are also fully colourable with RTP’s biocompatible colour products, which are also pre‐tested to ISO10993 compliance in precoloured resins and colour masterbatches. Additionally, these products are designated as change controlled formulae to ensure there is no modification to ingredients without customer authorisation.

The 6042 MD series of compounds have a shore A hardness range from 40 to 70 while the 6003 MD series have a range from 45 to 75. These products are formulated to bond with ABS, PC, PC alloys, PBT, rigid TPU, or co‐polyester substrates using either multi‐shot or insert moulding processes.

In a report submitted to Medical Plastics News, Elliott Pritikin, senior medical market manager at USA-headquartered elastomerics compounder Teknor Apex has written about why Medalist TPEs are an alternative option to “soft” flexible plastics like plasticised PVC, soft TPU and a range of rubbers.

Recognising industry concerns about traditional alternatives to PVC, such as inferior mechanical performance and overall “feel”, Pritkin says that Teknor Apex has taken a system approach to developing its Medalist brand of TPEs. Great emphasis has been placed on meeting “real-world” requirements that are not typically considered in a product data sheet.

Netherlands-based IMCD Group has announced that it has entered a new distribution partnership with Turkish compounder Elastron Kimya for their medical range of TPE-S and TPE-V compounds. The agreement is valid for all European countries and India. IMCD also distributes medical PVC compounds from US compounder Teknor Apex and medical TPUs from Taiwan’s Greco.

TPUs

In October 2012, Netherlands-headquartered high performance polymer manufacturer DSM revised and extended its existing licensing and supply agreement with AxioMed Spine Corporation, a US innovator in the field of implant devices used in spinal fusion and total disc replacement (TDR) procedures.

Under the agreement, DSM is supplying its proprietary CarboSil thermoplastic silicone-polycarbonate-urethane (TSPCU) copolymer for use in AxioMed’s soft implantable spinal discs.

DSM’s CarboSil TSPCU copolymer combines the flexibility and softness of a conventional silicone elastomer with the processability and strength of a thermoplastic polycarbonate-urethane.

AxioMed received CE Mark approvals in May 2012 for its Freedom Lumbar Disc and Freedom Cervical Disc brands of spinal implants in Europe. The Freedom Lumbar Disc device is the first elastomeric disc to receive an Investigational Device Exemption (IDE) from the US FDA. An IDE is a regulatory submission to the FDA that permits clinical investigations for medical devices. Devices covered by an IDE are exempt from legal restrictions related to shipping, making the device available on the market for investigational purposes only.

US chemical company and manufacturer of TPUs Lubrizol has launched an aromatic Carbothane TPU and has broadened its line of Tecothane soft polymers.

As an extension of Lubrizol’s Carbothane line of polycarbonate-based TPUs, new aromatic Carbothane is available in a range of grades and radiopacities.

Lubrizol says that unlike current technologies, aromatic Carbothane TPU features stronger material, improved chemical resistance and increased resistance to creep. These new products are suitable for some long-term implant applications, including catheters and devices introduced in the body for durations of more than 30 days, and for permanent implants used in spinal and orthopaedic applications.

The new aromatic Carbothane TPU from Lubrizol is available in four clear grades and four radiopaque grades. The latter include a 20% loading of barium sulfate. All grades of aromatic Carbothane carry all the necessary regulatory credentials.

Lubrizol has also broadened its line of Tecothane soft polymers designed specifically for healthcare and medical applications to include a wider range of material hardnesses.